The present disclosure relates to methods and apparatus for achieving a functional coating on a substrate, where the coating exhibits an elastic modulus gradient through a thickness thereof.
Many consumer and commercial products employ a sheet of high-quality cover glass to, for example, protect critical devices within the product, provide a user interface for input and/or display, and/or many other functions. For example, mobile devices, such as smart phones, mp3 players, computer tablets, etc., often employ one or more sheets of high strength glass on the product to both protect the product and achieve the aforementioned user interface. In such applications, as well as others, the glass may be durable (e.g., scratch resistant and fracture resistant), transparent, and/or antireflective. Indeed, in a smart phone and/or tablet application, the cover glass is often the primary interface for user input and display, which means that the cover glass would exhibit high durability and high optical performance characteristics.
Among the evidence that the cover glass on a product may manifest exposure to harsh operating conditions, scratches are probably the most common. Such evidence suggests that sharp contact, single-event damage is the primary source of visible scratches on cover glass in mobile products. Once a significant scratch mars the cover glass of a user input/display element, the appearance of the product is degraded and the resultant increase in light scattering may cause significant reduction in brightness, clarity and contrast of images on the display. Significant scratches can also affect the accuracy and reliability of touch sensitive displays. As a single severe scratch, and/or a number of moderate scratches, are both unsightly and can significantly affect product performance, they are often the leading complaint of customers, especially for mobile devices such as smart phones and/or tablets.
Accordingly, there are needs in the art for new methods and apparatus for achieving functional coatings on substrates, especially glass substrates.